Android活动例外 [英] Android Activity Exception

问题描述

我正在尝试在单击Button playlistBtn时启动一个新活动，并且我得到一个NullPointerException，但我看不出我的引用出错了。

请帮助。



这是错误消息：

java.lang.RuntimeException：无法启动活动ComponentInfo { app.and.androidmusic / app.and.androidmusic.PlaylistActivity}：java.lang.NullPointerException



MainActivity.java:

  public   class  MainActivity  extends  ListActivity {
 ... 
  protected   void  onCreate（Bundle savedInstanceState） {
  super  .onCreate（savedInstanceState）; 
 setContentView（R.layout.activity_main）; 
 ... 
 Button btnPlaylist =（Button）findViewById（R.id.playlistBtn）; 
 btnPlaylist.setOnClickListener（ new  View.OnClickListener（）{
  @ Override  
  public   void  onClick（查看arg0）{
意图=  new  Intent（getApplicationContext（），PlaylistActivity。 class ）; 
 startActivity（in）; 

PlaylistActivity：

  public  类 PlaylistActivity  extends  ListActivity {
 ... 
  @ Override  
  protected   void  onCreate（Bundle savedInstanceState）{
  super  .onCreate（savedInstanceState）; 
 setContentView（R.layout.activity_playlist） ; {

AndroidManifest.xml：

 <  活动  
   
                        < span class =code-attribute>   android：name   =  app.and.androidmusic.MainActivity  
   
              < span class =code-attribute>             android：label   =  @ string / app_name   < span class =code-keyword>>  
 <   intent-filter  >  
 <   action     android：name   =  android.intent.action.MAIN    /  >  
 <   category     android：name   =  android.intent.category.LAUNCHER    /  >  
 <   / intent-filter  >  
 <   / activity  >  
 <  活动  
   
                           android：name   = < span class =code-keyword>。播放列表活动    /  >  

解决方案

你可以写.PlaylistActivity，你能写全名吗？机器人：名称=app.and.androidmusic.PlaylistActivity

？

Hi, I''m trying to start a new activity when the Button playlistBtn is clicked, and I''m getting a NullPointerException, but I can''t see where did I go wrong with my references.
Please help.

This is the error message:
java.lang.RuntimeException: Unable to start activity ComponentInfo{app.and.androidmusic/app.and.androidmusic.PlaylistActivity}: java.lang.NullPointerException

MainActivity.java:

public class MainActivity extends ListActivity {
...
protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
...
Button btnPlaylist = (Button) findViewById(R.id.playlistBtn);
btnPlaylist.setOnClickListener(new View.OnClickListener() {					
                     @Override
	   		public void onClick(View arg0) {
			Intent in = new Intent(getApplicationContext(), PlaylistActivity.class);
						startActivity(in);

PlaylistActivity:

public class PlaylistActivity extends ListActivity{
...
@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_playlist); {

AndroidManifest.xml:

<activity

            android:name="app.and.androidmusic.MainActivity"

            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>        
        <activity

            android:name=".PlaylistActivity" />

解决方案

is it possible that you write .PlaylistActivity, could you write full name like android:name="app.and.androidmusic.PlaylistActivity?

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